Boll weevils are insects found in North, Central and South America which feed on cotton plants, causing serious damage to the plants and reducing harvest yield. Boll weevils develop through egg, larvae, pupae, and adult stages.
All life stages except the adult stage are spent inside cotton squares or bolls. Male boll weevils release an aggregating pheromone after feeding on cotton squares, and both males and females are attracted to this pheromone. Adult, overwintered females feed for 3 to 7 days, mate, and start laying eggs. Starting in the spring, females lay one egg per square or several in a boll. Each female usually lays an average of 150 eggs in her lifetime, each of which hatch in about three to five days. The resulting grubs or larvae feed about a week inside squares or bolls before changing into pupae; this stage lasts three to five days. Adults develop from pupae and cut their way out of squares or bolls. New adults feed from three to five days, mate, and begin laying eggs. These cycles are repeated during the season until the cotton plants are either destroyed or killed by frost. It is estimated that a single pair of weevils can generate up to two million offspring per year.
Numerous attempts have been made to trap, kill or destroy boll weevils. Farmers will often defoliate their crops to kill the weevils or at least remove their food source, and/or apply pesticides or insecticides over the crops to kill them. The insecticides are typically applied before pin-head square (before the cotton squares are one-third grown), so the weevils are killed before reproduction occurs.
The use of insecticides is associated with a variety of problems, including toxicity to humans and animals, and the relatively long half-life of a variety of insecticides. The chemicals can cause environmental pollution and also present health concerns for humans and animals which come into contact with the insecticides. Further, the chemicals often kill a variety of beneficial insects, including parasitic wasps, ladybugs and other insects that prey on the tobacco budwormn and other caterpillars that attack cotton.
There are currently eradication programs in at least seven states in the United States, and control and/or containment programs are being carried out in Mexico and every country in Central and South America where cotton is grown commercially. The eradication programs use various traps to attract and kill the boll weevils. The traps typically include Grandlure, a four-component mixture which functions as a synthetic pheromone for the boll weevil. In states where the boll weevil has been eradicated, pheromone-baited traps are used for survey purposes, to detect any new re-infestations. Use of the pheromone allows one to minimize the amount of insecticide used to kill the boll weevils, and to place the insecticide in a controlled location rather than broadly over an entire cotton field.
Examples of boll weevil attractant compositions including Grandlure are described, for example, in U.S. Pat. No. 3,803,303. Grandlure has been used in combination with feeding stimulants, poisons and other compounds, in a variety of different types of devices, for example, those described in U.S. Pat. No. 4,027,420. Polymeric compositions for attracting boll weevils using a sex attractant in combination with polyethylene glycol and a toxicant such as p-dichlorobenzene are disclosed, for example, in U.S. Pat. No. 3,803,303. The contents of these patents is hereby incorporated by reference. Plant attractants such as caryophylline oxide and beta-bisabalol have been used in some of these devices, where the attractant is applied to cotton dental-rolls. Other controlled-release dispensers have been developed to give long-term release of Grandlure (McKibben and Davich, Environmental Entomology, 6(6):804-806 (1977). Volatile compounds present in the cotton plant have been shown to attract boll weevils, although not when they are diapausing.
In the wintertime, boll weevils undergo certain physiological changes (entering a state of diapause) so that they can go without food during hibernation and survive the winter. Major changes in the boll weevil's body include accumulation of excess body fat, a reduction in water content, and cessation of reproduction. Diapausing boll weevils typically spend the winter near cotton fields, in woody areas, along ditch banks, and around trash and litter areas of cotton gins and old farm buildings. Development of diapausing weevils in fields usually continues until food supplies are destroyed, either by a killing frost or by defoliation and stalk destruction. Weevils entering diapause have been found as early as July; however, peak development of diapause usually coincides with the maturity of cotton plants.
Diapausing boll weevils are not as attracted to Grandlure as are reproductive boll weevils, so the traps are not effective at attracting and killing diapausing boll weevils. One method for controlling the population of diapausing boll weevils is defoliation. Defoliation is not necessary for effective diapause control, but defoliation enhances effectiveness of control by reducing food and breeding sites for later development of weevils. Typically, defoliants are applied within 10 to 14 days after the last application of an insecticide, or an insecticide such as methyl parathion, Guthion, malathion and/or various pyrethroids, is added to the defoliants. Since the cotton stalks are also a food source for the boll weevil, they are also typically destroyed.
In the summertime, male boll weevils produce enough of their pheromone that it competes with the traps, lessening their effectiveness. Accordingly, the eradication programs do not typically use the traps in the summer months.
It would be advantageous to provide compositions, devices and methods for attracting boll weevils and killing them or rendering them infertile year round, including in the winter when they are in a state of diapause, and in the summer, when the natural pheromone secreted by the male boll weevils competes with the Grandlure-baited traps.
Similar problems are also observed with respect to other insects which overwinter in areas with thick vegetation. It would also be useful to provide compositions, devices and methods for attracting these insects and optionally killing them or rendering them infertile. The present invention provides such compositions, devices and methods.